820-00597 iMac 21,5" 4K 2017 Not turning on

[iClub]

Hello, I have this board that is not turning on. The first LED is stable, the second one turns on for about 10 seconds and goes off. After about 3-4 seconds, the second LED turns on again, but this time it stays on. I honestly don't know if this is the standard switching behavior of this board (maybe?). But the third LED never turns on and things stop there. The board is very clean, with no signs of corrosion. CPU, GPU and PCH get a little warm. I have already tested another CMOS battery and other RAM memories, with no progress. I don't know exactly where to start on this board. Could you give me a hand? Thanks in advance.

 

[2informaticos]

Test the board removing CMOS battery.
Any fault history from client?

Which big coils get voltage?

 

[iClub]

I removed the battery, same behavior. No history from the client.

L7650: 5V
L7610: 3.3V
L9900: 1.35V
L9810: 0.8V
L9820: 0.8V
L9740: 0.8V
L7310: 1.1V (should drop below 1V?)
L7930: 0.9V
L7810: 1V
L7150: 1V
L7130: 1V
L7110: 1V
L7230: 0V
L7210: 0V
L8100: starts at 10V and drops slowly to 0V every time I plug in the power (without the display)
L7720: 1V
L9950: 1.8V
L6930: 3.3V
L9700: : 12V
L7000: 12V

Should i give a try on BIOS?

 

[2informaticos]

Known good BIOS is worth to try.
Also test with one DDR module at time, each RAM slot.

 

[iClub]

It was a BIOS problem, thanks for the help. It was a bit tricky to find a working version, I had to transplant the ME region of the client BIOS to a new BIOS version. I will provide the final version below.